Enthralled by a foreign saint, congregation develops (7)
I believe the answer is:
unfolds
'develops' is the definition.
(unfolding is a kind of developing)
'enthralled by a foreign saint congregation' is the wordplay.
'enthralled by' means one lot of letters goes inside another ('enthral' can mean 'capture').
'a foreign' becomes 'un' ('a' translated into French).
'saint' becomes 's'.
'congregation' becomes 'fold' ('fold' can be a synonym of 'congregation').
'un'+'s'='uns'
'uns' going around 'fold' is 'UNFOLDS'.
(Other definitions for unfolds that I've seen before include "(Of a story) develops" , "Gradually reveals" , "Opens, spreads out" .)